This invention lies in the field of elastic wave generation transmission and detection in the earth. More particularly it is concerned with determining the position in the earth of the bottom end of a long pipe extending into a deep borehole in the earth. Still more particularly, it concerns determination of the velocity of elastic waves in the earth.
In the prior art various means have been devised for logging deep boreholes in the earth. Most of these have been by the use of electrical methods in which currents are applied to the walls of the boreholes at selected depths and the corresponding potentials are measured in the earth. Also various instrumentations have been devised passively for measuring radiation in the earth, or for irradiating the earth with high energy radiation, and determining the response of the earth to this irradiation.
In regard to the use of elastic waves in the logging of boreholes, this has been confined principally to the use of low energy ultrasonic impulses applied at a selected point in a borehole and detecting the same energy after passing through a selected length of the rock walls of the boreholes. Unfortunately, the energy available in such logging systems has been quite small, and therefore the information that has been derived has been limited solely to the immediate area of the borehole at which the instrument is positioned.